1. Field of the Invention
The present invention relates to a method of depositing a gallium nitride-based III-V Group compound semiconductor crystal layer by the metalorganic chemical vapor deposition or metalorganic vapor phase epitaxy technique.
2. Description of the Related Art
Gallium nitride-based III-V Group compound semiconductor materials such as gallium nitride (GaN), gallium aluminum nitride (GaAlN), indium gallium nitride (InGaN), and indium aluminum gallium nitride (InAlGaN) are promising as materials for light-emitting devices. Recently, these compound semiconductors are grown by the metalorganic chemical vapor deposition (MOCVD), or metalorganic vapor phase epitaxy (MOVPE) technique.
However, gallium nitride-based III-V Group semiconductor materials having a good crystal quality can not be obtained efficiently by the conventional methods by the MOCVD or MOVPE technique.
The MOCVD or MOVPE technique has been discussed in many documents, including U.S. Pat. No. 4,368,098; Appl. Phys. Lett. 48(5), 3 Feb. 1986, pp. 353-355; Journal of Crystal Growth 68 (1984), pp. 163-168; Journal of Crystal Growth 93 (1988), pp. 216-219; Appl. Phys. Lett. 48(13), 31 Mar. 1986, pp. 870-872; Inst. Phys. Conf. Ser. No. 63: Chapter 10, 1981, pp. 479-484; and Journal of Crystal Growth 96 (1989), pp. 13-18.
Generally, the growth of gallium nitride-based III-V Group compound semiconductors such as GaN by MOVPE is effected through reaction of a gaseous organogallium material and a gaseous nitrogen-containing material on a heated substrate under atmospheric pressure. The substrate must be heated at a temperature at which the reactive gases can thermally decompose, so as to effect the reaction of the gaseous reactive materials on the surface of the substrate. Further, the gaseous reactive materials should be allowed to flow at high velocities, for example, 2 m/sec or more, in order to form a desired semiconductor crystal. Otherwise, sufficient amounts of the reactive gases cannot reach the surface of the substrate due to a large heat convection current generated by the high temperature of the substrate.
The high flow velocity of the reactive gases requires the use of a small diameter gas supply tube, which results in the formation of a semiconductor layer having a very small diameter, or having a very narrow width along the direction of the gas flow. The entire surface of the substrate can not be covered with a semiconductor layer formed by one growing operation.